Chain transfer behavior of fractionated commercial mercaptans in emulsion polymerization of styrene

The chain transfer behavior of fractionated commercial tertiary mercaptans was investigated in batch and semicontinuous emulsion polymerization of styrene over the entire monomer conversion range. Four mercaptans were obtained by fractionation, which contained 9, 11, 12, and 13 carbons, respectively. The effect of the mercaptans was evaluated in terms of the consumption rates of the monomer and the chain transfer agents, the number average degree of polymerization, DP_n, and the polydispersity index, I, of the polymer. The batch experiments showed that the chain transfer efficiency decreases with increasing carbon number, which is due primarily to a lower diffusion rate of the chain transfer agent to the reaction sites (growing latex particles) through the aqueous phase. The partitioning ratio of the chain transfer agents between the aqueous phase and the monomer droplets also contributes, to a lesser extent, to the efficiency. The number average degree of polymerization and the polydispersity index are primarily controlled by the ratio of the mercaptan consumption rate over that of the monomer. In order to obtain a polymer with a constant DP_n and a narrow I, this ratio should be as close to unity as possible, as is the case for C₁₁. Otherwise, too high a ratio causes a severe increase in DP_n at the end of polymerization, and too low a ratio leads in the opposite direction. The semicontinuous experiments confirmed the batch results. © 1994 John Wiley & Sons, Inc.     

Modeling the emulsion polymerization of amino-functionalized latex particles

A mathematical model for a semicontinuous seeded cationic emulsion polymerization was developed. The model includes the most distinctive features of the copolymerization of a cationic hydrophilic monomer with a hydrophobic one, including polymerization of the hydrophilic monomer in the outer shell of polymer particles and in the aqueous phase, and the possibility of having radical concentration profiles in the polymer particles.The reactions were carried out by means of a semicontinuous seeded cationic emulsion polymerization under starved conditions for styrene, which was the main monomer employed.The model predicts the evolution of the fractional overall conversions, the thickness of the outer shell, the total surface charge density and the partial conversions for the semicontinuous seeded cationic emulsion polymerization of styrene and aminoethyl methacrylate hydrochloride. Furthermore, the model can distinguish between the surface charge density provided by the cationic monomer than that given by the cationic initiator. Therefore, this model can predict the best conditions to obtain well-defined latexes with specific amounts of surface amino and amidine groups useful for immunoassays.     

Effect of acrylonitrile water solubility on the suspension copolymerization of acrylonitrile and styrene

Effect of acrylonitrile water solubility on the suspension polymerization of acrylonitile and styrene was investigated. It was found that the copolymer composition produced in the suspension polymerization of acrylonitrile and styrene was significantly different from that in the bulk polymerization at the same monomer feed ratio, since acrylonitrile is partially soluble in water. To predict accurately and then control the copolymer composition in the suspension polymerization, a model to calculate the copolymer composition was proposed based on considering the phase partition of actylonitrile between monomer and aqueous phases. The results calculated by the model are in agreement with the experimental data. The real reactivity ratios in monomer phase used in the model are the same as that in the bulk polymerization, but the apparent reactivity ratios used in the classical theory for the suspension polymerization vary significantly with water/oil ratio. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4270–4274, 2006     

Emulsion terpolymerization of dimethyl meta-isopropenyl benzyl isocyanate (TMI®) with acrylic monomers: Process development and kinetics

Dimethyl meta-isopropenyl benzyl isocyanate (TMI®) is a bifunctional monomer possessing a double bond and an isocyanate group. Emulsion terpolymerization of TMI with the acrylic monomers, methyl methacrylate and n-butyl acrylate, was studied. Polymerizations were carried out at 40°C using a redox initiator system in order to minimize the extent of hydrolysis of the isocyanate in the aqueous emulsion environment. The kinetics of the polymerization reaction were investigated. The polymerization rate was found to decrease with increasing TMI concentration. The effects of several preparative variables such as the monomer, surfactant, and initiator concentration on the polymerization kinetics was studied. Several semicontinuous polymerization processes were developed in order to enhance the incorporation of TMI at appreciable rates. These processes also allow us to control the polymer composition, latex particle size, and the locus of isocyanate groups in the latex particle. Process variables such as the mode of initiator addition (batch versus semicontinuous) were found to greatly influence the polymerization behavior. © 1996 John Wiley & Sons, Inc.     

A comparison of methods for the estimation of polymer/monomer interaction parameters: The polystyrene/n-butyl methacrylate system methacrylate system

To measure the polymer/monomer interaction parameter as a function of composition, a set of partially cross-linked synthetic latices has been produced by batch and semicontinuous emulsion polymerization. The degrees of cross-linking have been measured by DMA and also predicted by computer simulation based on kinetic data. With equilibrium monomer swelling experiments achieved on films made from these polymers, two curves of the interaction parameter vs. the polymer fraction have been computed. These curves compare favorably with a theoretical model based on a Unifac procedure for the estimation of monomer activity. Two different data bases, liquid-liquid and liquid-vapor equilibria, have been used in the Unifac model. For the polystyrene/n-butyl methacrylate system, a linear relationship found between the interaction parameter and composition is both predicted and measured experimentally. In all cases, this interaction parameter is found to increase with polymer concentration. © 1994 John Wiley & Sons, Inc.     

On loci of acrylonitrile polymerization with bisulfite-persulfate initiators under the conditions of low water/monomer ratio

In the preparation of acrylonitrile–vinylacetate copolymer (93:7 in weight) by continuous polymerization in aqueous medium using the complete mixing type reactor, the author and co-workers studied the effects of the water/monomer ratio on polymer properties and polymerization. They reported that the structure of a polymer particle becomes more compact with decreasing water/monomer ratio. This was noted in studying the physical properties of the polymer and the formation of polymer particles in this system. ^1,2 Here the author has performed kinetic studies based on the results of polymerization to determine the loci of the polymerization in the range of water/monomer ratio roughly from 1.75 to 4.0. Most of the primary radicals from the initiators attack the monomers in the aqueous phase to form monomer radicals attached to initiator fragments, and most of the monomer radicals grow to form polymer radicals until termination occurs in the aqueous phase. Hence, the loci of polymerization in this system are not the surfaces and inner parts of the polymer particles, the diameters of which are roughly from 20 to 60 μm observed by a microscope, but the aqueous phase excluding these particles.     

Seeded emulsion polymerization of n-butyl acrylate utilizing miniemulsions

Nucleation of polymer particles in the seeded emulsion polymerization of n-butyl acrylate (BuA) was studied through experiments designed to control the amount of new particles formed. The results show that for the batch and semicontinuous seeded polymerization of BuA, a small amount of new particles was formed in the system in which the monomer was added neat, whereas a singificant amount of new particles was formed when the monomer was added as a miniemulsion. This suggests that new particles formed in the miniemulsion process were from nucleation of the monomer droplets. These experiments also showed that monomer-droplet nucleation decreased with increasing seed concentration in the reactor. For the seeded semicontinuous polymerizations, monomer-droplet nucleation decreases with decreasing BuA miniemulsion feed rate. The results also show that monomerdroplet nucleation takes place whenever miniemulsion droplets exist in the reactor. This study suggests that miniemulsions can be used to control the particle size distribution of a polymer latex system.     

Copolymer composition control by means of semicontinuous emulsion copolymerization

The effect of two different monomer addition strategies on the chemical composition distribution of the copolymer formed by the (seeded) semicontinuous emulsion copolymerization of styrene and methyl acrylate has been investigated. 1. The addition of a mixture of the monomers at a constant feed rate results in a homogeneous copolymer, provided that extremely long process times are used (starved conditions). When not starting from a seed latex, aqueous phase polymerization was observed at low feeding rates. When using a seed latex, aqueous phase polymerization appeared to be negligible. 2. In order to achieve an optimal monomer addition pattern, a pragmatic approach is presented. An optimal monomer addition profile was calculated from accurate monomer partitioning data using a short iteration procedure. Gradient high performance liquid chromatography (HPLC) was successfully applied as a rigorous test of the homogeneity of the copolymer formed. The information obtained contains much more detail than in the case of using differential scanning calorimetry of ¹H NMR. In contrast to ¹H NMR that provides only average cumulative chemical compositions, the complete chemical composition distribution can be obtained by means of HPLC.     

Emulsion copolymerization: Kinetics model and reactor performance

The Dow process for producing perfluorinated ionomeric membranes includes several emulsion copolymerizations involving gaseous tetrafluoroethylene and a second liquid phase monomer. The choice of the organic phase monomer depends on the desired product. The emulsion copolymerization reactor model was developed by extending the Smith-Ewart-Gardon theory for emulsion polymerization processes. Population balance techniques and Flory-Huggins solution theory were applied. The resulting coupled partial differential equations were solved using the method of characteristics. The reactor model, with minimal adjustable parameters, predicts most polymerization results, including molecular weight, reaction rates in the three process stages, latex particle size, polymer composition, and the composition drift as a function of reaction time. The analysis and reactor model is used in the manufacturing process to set process conditions to obtain the desired properties in the polymer product.     

MMA-EA-DM三元共聚胶乳的制备及共聚物表征

以 ( NH4) 2 S2 O8-Na2 SO3 为氧化还原引发体系 ,用种子与无种子半连续乳液聚合两种方法 ,于4 5～ 6 5℃ ,进行甲基丙烯酸甲酯 ( MMA) -丙烯酸乙酯 ( EA) -甲基丙烯酸二甲胺基乙酯 ( DM)三元乳液共聚合。结果表明采用无种子半连续乳液聚合法所得乳液稳定性好 ,其转化率可达 99% ,共聚物的特性粘数为4 .1 2 dl/ g。对共聚物进行 IR、1 HNMR的研究结果表明由于单体 DM溶于水 ,三元乳液共聚合时 ,基本上合成的是三元共聚物 ,其组成比为 1∶ 1∶ 0 .75 ( mole) ,有极少部分的 DM的均聚物或者是富集 DM的共聚物生成 ,其摩尔百分数为 3.6 %。     

Simulation of kinetic analysis on terpolymerization of styrene/butyl methacrylate/methacrylic acid system

The simultaneous differential equations which connected the copolymerization kinetics of the component reaction in the multi-copolymerization system with the changing rate of the concentration of each monomer and radical, the concentration and the molecular weight of the polymer obtained are analysed in a number of ways. The distribution of the components and the degree of polymerization are also simulated. The styrene/butyl methacrylate/methacrylic acid terpolymerization system, using carbon tetrachloride as solvent and benzoyl peroxide as initiator, was chosen. The simulation model which satisfied the experimental values of the concentration of the multiple components in the system, the composition and molecular weight distribution and the number of chlorine atoms introduced into the copolymer ends is established. When the time interval changed, the effects on the distribution of the composition in copolymers and the distribution of the degree of polymerization were also calculated.     

丙烯酰胺水溶液聚合反应的研究

探讨了聚乙二醇作为分散剂时丙烯酰胺水溶液聚合体系中单体含量、还原剂用量对聚合物分子量的影响，并探讨了聚合时间与转化率、单体含量与聚合体系粘度之间的关系。结果表明，在保持聚合体系能够流动的前提下，单体含量可提高到２０％，聚合物的分子量可达３００万以上。     

Study on the effective process parameters influencing styrene and acrylonitrile grafting onto seeded polybutadiene latex

A series of experiments were designed and conducted to determine the significance of process parameters in the grafting of styrene and acrylonitrile onto polybutadiene seeds in a semicontinuous emulsion copolymerization system. The significances of the parameters were obtained by comparing the variance ratios, or F values, with F‐distributions. The significance level of each test (α‐value) was obtained by variance analysis. The important process parameters in industrial polymerization processes are usually monomer‐to‐polymer ratio, initiator type and concentration, chain‐transfer agent, and reaction temperature. The target responses were final monomer conversion, grafting degree, grafting efficiency, gel percent, and viscosity‐average molecular weight of free styrene‐acrylonitrile (SAN). The analysis of variance indicated that cumene hydroperoxide as the initiator and reaction temperature had strong effects on the graft structure. Moreover, free SAN molecular weight was significantly affected by the monomer/polymer ratio and cumene hydroperoxide and n‐dodecyl mercaptan as chain‐transfer agents. The raspberry‐like morphology of grafted acrylonitrile‐butadiene‐styrene (ABS) particles and phase separation within the particles were confirmed by transmission electron microscopy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Tunable mechanical properties of core‐shell polymers of poly(hexyl methacrylate) and poly(methyl methacrylate) by semicontinuous heterophase polymerization

The synthesis of core/shell polymers with tunable mechanical properties made of poly(hexyl methacrylate) (PHeMA) and poly(methyl methacrylate) (PMMA) by a two‐stage semicontinuous heterophase polymerization, is presented here. This polymerization technique is characterized by employing low surfactant concentrations to produce large polymer‐to‐surfactant ratios. In this process, monomer is added in a continuous low rate to achieve monomer starved conditions, allowing to control particle size (usually smaller than 50 nm). To modulate the mechanical properties, the weight ratio of core/shell polymers are varied from 10/90 to 90/10 for direct and reverse compositions, respectively. Conversion was followed gravimetrically; nanoparticles were characterized with quasi‐elastic light scattering, IR spectroscopy, differential scanning calorimetry, transmission electron microscopy, and mechanical tests (tensile and hardness). Highly stable latex formed of nanoparticles, with high conversions are obtained. Tensile tests show that the mechanical properties can be tuned according to core/shell composition, mainly in the system formed by PMMA/PHeMA. These results are explained in terms of core‐and‐shell polymers location, composition and hardness. As expected, an increment in concentration of PMMA produces a more rigid material independently of its position. POLYM. ENG. SCI., 59:365–371, 2019. © 2018 Society of Plastics Engineers     

Modeling of diffusion-controlled free-radical polymerization reactions

The present paper introduces a new fundamental approach to the modeling of diffusion-controlled free-radical polymerization reactions. Our analysis follows the original work of Chiu, Carratt, and Soong (CCS), according to which the termination and propagation rate constants are expressed in terms of both a purely reaction-limited term and a diffusion-limited one. The contribution of the latter term to the apparent rate constants is described in terms of the polymer and monomer effective diffusion coefficients and an effective reaction radius. It is shown that all parameters appearing in the original CCS model can be calculated from first principles using available data on the physical and transport properties of a particular monomer–polymer binary system. The generalized free volume theory of Vrentas and Duda and the theory of excess chain end mobility are invoked for the calculation of the effective diffusion coefficients and the reaction radius, respectively. The approach followed in this study is general and needs only the specification of one unknown parameter with a clear physical meaning. All other parameters can be readily calculated from available data. The ability of the new model to predict molecular weight developments and monomer conversion in diffusion-controlled reactions is demonstrated by application of the proposed model equations to the bulk polymerization of MMA.     

乳液聚合导致一种新的转相过程

借助电导率仪、光学显微镜和亚微粒子分析仪等测试手段。研究了乳液聚合导致一种新的转相过程,并用于八甲基环四硅氧烷的聚合中。研究表明:体系以 W/O 相态开始,单体由连续相向水相(分散相)内的胶束中扩散并发生聚合反应,形成 O/W/O 复合乳液。反应过程中连续相体积不断减小,分散相(O/W 复相)体积不断增大,当达到某一临界相比时,体系发生转相,转相后乳液为 O/W。对本实验物系,转相点临界相比主要由初始水油比和乳化剂浓度决定。同常规的乳液聚合相比,伴有转相现象的乳液聚合有其自身的特点,转相使得聚合速率、聚合物粒径及分布、乳液稳定性等发生变化。     

Rate of emulsion polymerization of styrene

In emulsion polymerization, the Smith and Ewart theory gives about two or three times the number of polymer particles obtained by experiment. In this paper, a reaction model is proposed which, from the standpoint of reactor design, can give an adequate explanation of the whole course of an emulsion polymerization of monomer highly insoluble in water. Among other things, the generating process of polymer particles is examined in detail. It is demonstrated experimentally that a new parameter proposed here, which represents the degree of difficulty of monomer initiation in micelles, is indispensable in explaining that process. Also confirmed is that monomer initiation takes place more easily in polymer particles than in micelles. According to the new model, the progress of polymerization, i.e., monomer conversion, the number of the polymer particles, and properties of polymer thus produced can be estimated with satisfactory accuracy. Furthermore, approximate equations are derived for easier estimation.     

Batch and semicontinuous emulsion copolymerization of vinylidene chloride and butyl methacrylate. I. Kinetics in VDC–BMA emulsion polymerization and surface and colloidal properties of VDC–BMA latexes

Vinylidene chloride (VDC)—butyl methacrylate (BMA) comonomer mixtures with various composition (83 : 17, 60 : 40, 33 : 67 in mol %) were polymerized at 25°C using redox catalyst by batch and seeded semicontinuous emulsion copolymerization. The reactivity ratios determined in VDC (M₁)—BMA (M₂) emulsion copolymerization system were r₁ = 0.22 and r₂ = 2.41. Seven 35% solids (83 : 17 mol %) VDC–BMA copolymer latexes were prepared: one batch (G), one seeded batch (F), and 5 seeded semicontinuous polymerizations of 5 different monomer feed rates ranging from 0.27 (A) to 1.10 wt %/min (E). The kinetic studies of seeded semicontinuous polymerizations A-E showed that the rates of polymerizations (R_p) were controlled by the monomer addition rates (R_a). The conversion versus time curves for the polymerizations of 0 : 100–100 : 0 VDC–BMA mixtures by batch polymerization showed that the rate of polymerization (R_p) was a function of the number of particles, and that the rate of polymerization in a latex particle (R_pp) increased with increasing proportions of butyl methacrylate in the monomer mixture. All of the latexes had narrow particle size distributions. The greater particle number density in VDC polymerization and the greater water solubility of VDC suggest that the homogeneous nucleation mechanism is operative in VDC–BMA copolymerizations. The latex copolymers prepared by semicontinuous polymerization had lower number-and weight-average molecular weights than those of the corresponding batch copolymers, resulting from the monomer starvation occurring during the semicontinuous polymerization. The surface characterization study of the cleaned latexes showed that for the latexes by batch process, the surface charge density derived from strong-acid groups decreased with increasing proportion of VDC in the monomer mixture. On the other hand, for the latexes prepared by semicontinuous polymerization, the surface charge density derived from strong-acid groups did not depend on the monomer composition of the copolymers.     

偏二氯乙烯-丙烯腈悬浮共聚动力学

研究了单体配比、引发剂浓度、聚合温度、转化率等因素对偏二氯乙烯(VDC)-丙烯腈(AN)悬浮共聚树脂的组成、相对分子质量和聚合速率的影响,建立了动力学模型,讨论了AN的水溶性对树脂组成的影响,提出了相对分子质量与聚合温度及引发剂浓度关系的模型。     

Polymer particles with a pomegranate-like internal structure via micro-dispersive polymerization in a geometrically confined reaction space I. Experimental study

The synthesis of micron-sized polymer particles with a core-shell pomegranate-like morphology is presented. The proposed polymerization technique takes advantage of a reaction-induced micro-phase separation within a suspended organic liquid droplet containing monomer, a chemical initiator, a steric stabilizer, and a poor solvent for the polymer. With an increase in monomer conversion, the monomer droplet suspended in a continuous aqueous medium is transformed first into a micro-capsule with a thick pericellular membrane, and eventually into a polymer particle packed with 300-500 nm polymer sub-particles. The experimentally observed evolution of particle morphology indicates that the reaction pathway is strongly influenced by micro-phase separation and transport phenomena. In the first stage of polymerization, a pseudo-homogeneous polymerization takes place at the droplet surface, followed by a starved macro-dispersive polymerization in the inner region where polymer precipitates out from the solvent phase as nano-sized sub-particles.